Pubic symphysis

The pubic symphysis (or symphysis pubis) is a midline secondary amphiarthrodial, fibrocartilaginous joint of the bony pelvis, uniting both pubic bodies.

Gross anatomy

Articulations

The pubic symphysis is a secondary cartilaginous joint, which means there is a wedge-shaped fibrocartilaginous interpubic disc situated between two layers of hyaline cartilage, which line the oval-shaped medial articular surfaces of the pubic bones ^1-2. 

The width of the joint space differs at different ages:

• ~10 mm at 3 years
• ~6 mm at 20 years
• ~3 mm at 50 years

For physiological reasons, women have a greater thickness of the fibrocartialginous disc, allowing more mobility of the pelvic bones and thereby providing a larger pelvic diameter needed for childbirth.

Attachments

Ligaments

The pubic symphysis is reinforced by four strong ligaments ^2-3:

• superior pubic ligament - runs from pubic crest to pubic crest
• inferior pubic (or subpubic or arcuate) ligament - runs from inferior pubic ramus to inferior pubic ramus
• anterior pubic ligament - blends with periosteum laterally as well as the interpubic disc
• posterior pubic ligament - blends with periosteum of both pubic bodies posteriorly

Musculotendinous

• adductor longus, adductor brevis and rectus abdominis muscles attach to the anterior pubic ligament and interpubic disc ²
• external oblique aponeurosis also reinforces the pubic symphysis anteriorly ³

Relations

• anteriorly
  • proximal ends of the penile/clitoral shafts
• inferiorly
  • urethra
  • deep dorsal vein of penis/clitoris
• posteriorly
  • bladder (separated from pubic symphysis by the retropubic fat pad)
  • prostate and prostatic venous plexus

Movement

Normally very little movement - up to 2mm shift and 1 degree rotation ². 

Blood supply

• mainly supplied by branches of obturator and inferior epigastric arteries ²

Nerve supply

• supplied by branches of the pudendal and/or genitofemoral and/or iliohypogastric/ilioinguinal nerves ²

Variant anatomy

• congenital widening of the pubic symphysis (rare) ⁵

Radiographic appearance

CT/MRI

• due to anteriorly-situated secondary ossification centres may appear "V-shaped" in adolescents on axial slices but will normally be parallel in adults ¹

Related pathology

• parturition-induced pelvic instability
• pubic symphysis widening (mnemonic)
• open book fracture of the pelvis
• osteitis pubis
• pubic symphysis fusion (or bridging)